Class WithinPosition

Arguments:
o position - The default integer position
o left - The start (left) position of the boundary
o right - The end (right) position of the boundary

This allows dealing with a position like ((1.4)..100). This
indicates that the start of the sequence is somewhere between 1
and 4. Since this is a start coordinate, it should acts like
it is at position 1 (or in Python counting, 0).

The old legacy properties of position and extension give the
starting/lower/left position as an integer, and the distance
to the ending/higher/right position as an integer. Note that
the position object will act like either the left or the right
end-point depending on how it was created: